Multi-stage additive manufacturing system

ABSTRACT

An additive manufacturing system is disclosed. The additive manufacturing system may include a first print stage configured to discharge a first type of composite structure. The additive manufacturing system may also include a second print stage configured to discharge a second type of composite structure. The additive manufacturing system may further include a support configured to move the first and second print stages.

RELATED APPLICATIONS

This application is based on and claims the benefit of priority from U.S. Provisional Application No. 62/459,398 that was filed on Feb. 15, 2017, the contents of which are expressly incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a manufacturing system and, more particularly, to a multi-stage additive manufacturing system.

BACKGROUND

Pultrusion is a common way to manufacture composite parts. During pultrusion manufacturing, individual fiber strands, braids of strands, and/or woven fabrics are pulled from corresponding spools into a resin bath and through a stationary die. The resin is then allowed to cure and harden. Due to the pulling of the fibers prior to curing, some of the fibers may retain a level of tensile stress after curing is complete. This tensile stress can increase a strength of the composite part in the direction in which the fibers were pulled.

A vacuum-assisted resin transfer molding (VARTM) process is commonly used to fabricate the skin of a large composite structure (e.g., of a vehicle body), after an internal skeleton has already been formed (e.g., via pultrusion). In a VARTM process, sheets of fibrous material are manually pulled over the internal skeleton and then tacked in place. The tacked material is then manually coated with a liquid matrix (e.g., a thermoset resin or a heated thermoplastic), covered with a vacuum bag to facilitate impregnation of the liquid matrix, and allowed to cure and harden.

Although pultrusion manufacturing and VARTM can be used together to produce some large composite parts, they can also be problematic. In particular, the VARTM-produced skin is often attached to the pultruded skeletal components and/or reinforced via metallic fasteners (e.g., screws, rivets, and clips). The use of metallic fasteners can drive skeletal design and increase a weight and cost of the part. In addition, the various components of the large composite part may need to be joined to each other via specially designed hardware, which can also be heavy and costly. Further, a significant delay may be required between fabrication of the internal skeleton and the skin, in order to allow for the internal skeleton to fully cure. Finally, conventional pultrusion and VARTM manufacturing processes may provide little flexibility in the design and/or use of the composite part.

The disclosed additive manufacturing system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to an additive manufacturing system. The additive manufacturing system may include a first print stage configured to discharge a first type of composite structure. The additive manufacturing system may also include a second print stage configured to discharge a second type of composite structure. The additive manufacturing system may further include a support configured to move the first and second print stages.

In one aspect, the present disclosure is directed to a method of additive manufacturing. The method may include discharging from a first type of print head a first type of composite structure. The method may also include simultaneously discharging from a second type of print head a second type of composite structure adjacent the first type of composite structure.

In one aspect, the present disclosure is directed to another method of additive manufacturing. This method may include discharging a plurality of composite tubes adjacent each other to form an internal skeleton in the shape of boat hull. The method may also include simultaneously discharging a composite skin over the plurality of composite tubes. A matrix in the plurality of composite tubes may not be fully cured when the composite skin is discharged over the plurality of composite tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary system for additively manufacturing a composite part; and

FIGS. 2-4 are isometric illustrations of exemplary applications of the system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system 10 for additively manufacturing a composite component 12. System 10 may implement any number of different additive processes during manufacture of component 12. For example, component 12 is shown in FIG. 1 as being manufactured via a first additive process (represented in the lower-left of FIG. 1) and via a second additive process (represented in the upper-right of FIG. 1). It should be noted that the first and second additive manufacturing processes may be performed simultaneously or consecutively, as desired. It should also be noted that component 12 may be manufactured utilizing only one of the first and second additive processes.

The first additive process may be a pultrusion and/or extrusion process, which creates hollow tubular structures 14 from a composite material (e.g., a material having a matrix and at least one continuous reinforcement). One or more heads 16 may be coupled to a support 18 (e.g., to a robotic arm) that is capable of moving head(s) 16 in multiple directions during discharge of structures 14, such that resulting longitudinal axes 20 of structures 14 are three-dimensional. Such a head is disclosed, for example, in U.S. patent application Ser. Nos. 15/130,412 and 15/130,207, all of which are incorporated herein in their entireties by reference.

Head(s) 16 may be configured to receive or otherwise contain the matrix material. The matrix may include any type of liquid resin (e.g., a zero-volatile organic compound resin) that is curable. Exemplary matrixes include thermosets, single- or multi-part epoxy resins, polyester resins, cationic epoxies, acrylated epoxies, urethanes, esters, thermoplastics, photopolymers, polyepoxides, thiols, alkenes, thiol-enes, and more. In one embodiment, the pressure of the matrix inside of head(s) 16 may be generated by an external device (e.g., an extruder or another type of pump) that is fluidly connected to head(s) 16 via corresponding conduits (not shown). In another embodiment, however, the pressure may be generated completely inside of head(s) 16 by a similar type of device and/or simply be the result of gravity acting on the matrix. In some instances, the matrix inside head(s) 16 may need to be kept cool and/or dark, in order to inhibit premature curing; while in other instances, the matrix may need to be kept warm for the same reason. In either situation, head(s) 16 may be specially configured (e.g., insulated, chilled, and/or warmed) to provide for these needs.

The matrix stored inside head(s) 16 may be used to coat any number of continuous reinforcements and, together with the reinforcements make up walls of composite structures 14. The reinforcements may include single strands, a tow or roving of several strands, or a weave of many strands. The strands may include, for example, carbon fibers, vegetable fibers, wood fibers, mineral fibers, glass fibers, metallic wires, ceramic fibers, basalt fibers, optical tubes, etc. The reinforcements may be coated with the matrix while the reinforcements are inside head(s) 16, while the reinforcements are being passed to head(s) 16, and/or while the reinforcements are discharging from head(s) 16, as desired. In some embodiments, a filler material (e.g., chopped fibers, metallic or ceramic particles, etc.) may be mixed with the matrix before and/or after the matrix coats the reinforcements. The matrix, the dry reinforcements, reinforcements already coated with the matrix, and/or the filler may be transported into head(s) 16 in any manner apparent to one skilled in the art. The matrix-coated reinforcements may then pass over a centralized diverter (not shown) located at a mouth of head(s) 16, where the matrix is caused to cure (e.g., from the inside-out, from the outside-in, or both) by way of one or more cure enhancers (e.g., UV lights, ultrasonic emitters, microwave generators, infrared heaters, chillers, etc.) 22.

In embodiments where component 12 is made up of multiple structures 14, each structure 14 may be discharged adjacent another structure 14 and/or overlap a previously discharged structure 14. In this arrangement, subsequent curing of the liquid matrix within neighboring structures 14 may bond structures 14 together. Any number of structures 14 may be grouped together and have any trajectory, shape, and size required to generate the desired shape of component 12.

In some embodiments, a fill material (e.g., an insulator, a conductor, an optic, a surface finish, etc.) could be deposited inside and/or outside of structures 14, while structures 14 are being formed. For example, a hollow shaft (not shown) could extend through a center of and/or over any of the associated head(s) 16. A supply of material (e.g., a liquid supply, a foam supply, a solid supply, a gas supply, etc.) could then be connected with an end of the hollow shaft, and the material forced through the hollow shaft and onto particular surfaces (i.e., interior and/or exterior surfaces) of structure 14. It is contemplated that the same cure enhancer(s) 22 used to cure structure 14 could also be used to cure the fill material, if desired, or that additional dedicated cure enhancer(s) (not shown) could be used for this purpose. The fill materials could allow one or more of structures 14 to function as tanks, passages, conduits, ducts, etc.

The second additive manufacturing process may also be a pultrusion and/or extrusion process. However, instead of discharging hollow tubular structures 14, the second additive manufacturing process may be used to discharge tracks, ribbons, and/or sheets 23 of composite material (e.g., adjacent tubular structures 14 and/or over other features of component 12). In particular, one or more heads 24 may be coupled to a support 26 (e.g., to an overhead gantry) that is capable of moving head(s) 24 in multiple directions during fabrication of component 12, such that resulting contours of component 12 are multi-dimensional (e.g., three-dimensional).

Head 24 may be similar to head 16 and configured to receive or otherwise contain a matrix material (e.g., the same matrix contained within head 16 or a different matrix). The matrix stored inside head(s) 24 may be used to coat any number of separate reinforcements, allowing the reinforcements to make up centralized cores of the discharging tracks, ribbons, and/or sheets 23. The reinforcements may include single strands, a tow or roving of several strands, or a weave of multiple strands. The strands may include, for example, carbon fibers, vegetable fibers, wood fibers, mineral fibers, glass fibers, metallic wires, optical tubes, etc. The reinforcements may be coated with the matrix while the reinforcements are inside head(s) 24, while the reinforcements are being passed to head(s) 24, and/or while the reinforcements are discharging from head(s) 24, as desired. The matrix, the dry reinforcements, and/or reinforcements already coated with the matrix may be transported into head(s) 24 in any manner apparent to one skilled in the art. The matrix-coated reinforcements may then pass through one or more circular orifices, rectangular orifices, triangular orifices, or orifices of another curved or polygonal shape, where the reinforcements are pressed together and the matrix is caused to cure by way of one or more cure enhancers 22.

As described above, the first and second additive manufacturing processes can be extrusion or pultrusion processes. For example, extrusion may occur when the liquid matrix and the associated continuous reinforcements are pushed from head(s) 16 and/or head(s) 24 during the movement of supports 18 and/or 26. Pultrusion may occur after a length of matrix-coated reinforcements is connected to an anchor (not shown) and cured, followed by movement of head(s) 16 and/or head(s) 24 away from the anchor. The movement of head(s) 16 and/or head(s) 24 away from the anchor may cause the reinforcements to be pulled from the respective head(s), along with the coating of the matrix material.

In some embodiments, pultrusion may be selectively implemented to generate tension in the reinforcements that make up component 12 and that remains after curing. In particular, as the reinforcements are being pulled from the respective head(s), the reinforcements may be caused to stretch. This stretching may create tension within the reinforcements. As long as the matrix surrounding the reinforcements cures and hardens while the reinforcements are stretched, at least some of this tension may remain in the reinforcements and function to increase a strength of the resulting composite component 12.

Components fabricated via conventional pultrusion methods may have increased strength in only a single direction (e.g., in the single direction in which fibers were pulled through the corresponding die prior to resin impregnation and curing). However, in the disclosed embodiment, the increased strength in component 12 caused by residual tension within the corresponding reinforcements may be realized in the axial direction of each of the reinforcements. And because each reinforcement could be pulled in a different direction during discharge from head(s) 16 and/or 24, the tension-related strength increase may be realized in multiple (e.g., innumerable) different directions.

Components fabricated via conventional pultrusion methods may have strength increased to only a single level (e.g., to a level proportionate to an amount in which the reinforcements were stretched by a pulling machine prior to resin impregnation and curing). However, in the disclosed embodiment, because the matrix surrounding each reinforcement may be cured and harden almost immediately upon discharge, the force pulling on the reinforcement may be continuously varied along the length of the fiber, such that different segments of the same reinforcement are stretched by different amounts. Accordingly, the residual tensile stress induced within each of the different segments of each different reinforcement may also vary, resulting in a variable strength within different areas of component 12. This may be beneficial in variably loaded areas of component 12.

FIG. 2 illustrates a large-scale application of system 10. In this application, a plurality of heads 16 are connected to work together (e.g., in a chain configuration) in one or more stages of fabrication, while a plurality of heads 24 are connected to work together in one or more subsequent stages of fabrication. Within each stage of fabrication, heads 16 and heads 24, within their respective stage(s), may be located adjacent each other and collectively moved, oriented, and/or positioned by a common support 18 and/or 26 during material discharge. In this way, a larger portion (e.g., one or more layers of an entire cross-section) of component 12 may be fabricated simultaneously.

For example, a first stage S₁ involving multiple heads 16 may be used to fabricate adjacent tubular structures 14 that make up a rough internal skeleton at a relatively fast rate. A second stage S₂ involving multiple heads 24 may follow behind the first stage S₁ and create finer (e.g., smaller and closer together) constructions (e.g., a skin from fibers, ribbons and/or sheets 23) with greater accuracy on top of the larger constructions created by the first stage S₁ (over structures 14). In one embodiment, the second stage S₂ may follow a distance D₁ behind the first stage S₁, such that the matrix discharged in the first stage S₁ is not yet fully cured (e.g., such that the matrix is still tacky) when the matrix-coated reinforcements of the second stage S₂ are discharged adjacent structures 14. In this manner, cross-linking between the internal skeleton of stage S₁ and the covering of stage S₂ may be enhanced. It is contemplated that any number of the first and second stages S₁, S₂ may be used to fabricate a single structure (e.g., stages that create larger and smaller overlapping tubular structures 14; stages that create thicker or thinner outer skins; and/or stages that create intermediate skins), and that the stages could be choreographed in any order.

In some embodiments, any number of third stages S₃ may follow behind the first and/or second stages S₁, S₂. In these embodiments, the third stage S₃ may be a finish stage focused on creating a final surface texture, tint, and/or sealant coat on top of structures 14 and/or the outer skin. For example, the third stage S₃ may provide for a layer of matrix-coated chopped fibers, a layer of only matrix, a layer of paint, a layer of insulation, a gel coat, a clear coat, etc. to be deposited onto the materials discharging from stages S₁ and/or S₂. In one embodiment, the third stage S₃ may follow a distance D₂ behind the second stage S₂, such that the matrix discharged in the second stage S₂ is fully cured when the material(s) of the third stage S₃ are discharged over the top of the material(s) of the second stage S₂. In the example of FIG. 2, an entire boat hull may be created by the time the first, second, and third stages S₁, S₂, S₃ are complete.

A similar large-scale embodiment (also associated with boat fabrication) is illustrated in FIG. 3. The boat hull of this embodiment may be fabricated in much the same manner as in the embodiment of FIG. 2. However, in contrast the previous embodiment, the boat hull of FIG. 3 may include internal bulkheads 30 that are interspersed with tubular structures 14. It is contemplated that bulkheads 30 may be prefabricated or fabricated in-situ, as desired. For example, bulkheads 30 may be cut from wood, injection molded from a thermoplastic (e.g., a fiber-reinforced thermoplastic), and/or fabricated via the first and/or second processes described above.

If fabricated separately, bulkheads 30 may be stood up and moved to designated locations prior to the first stage S₁ (described above) being initiated. Bulkheads 30 may then become starting and/or ending anchor points (also described above) for tubular structures 14. For example, as shown in FIG. 4, each bulkhead 30 may be sandwiched and chemically bonded in place between ends of opposing tubular structures 14. The skin may then be formed fibers, ribbons, and/or sheets 23 over an outer annular surface of bulkheads 30 during formation on top of tubular structures 14. This may help create stiff connections between the separate components.

If fabricated in-situ using the disclosed system 10, bulkheads 30 may be formed from one or more tubular structures (e.g., a single structure that extends the entire length) 14 and/or fiber strands, ribbons, and/or sheets. Bulkheads 30 that are fabricated in this manner may be only partially cured prior to inclusion within the rest of the boat hull, so as to improve bonding with the other tubular structures 14 and/or skin 14. It is contemplated that additional tubular structures 14 could be arranged as internal and/or external layers that pass over the outside and/or inside of bulkheads 30, if desired. In one embodiment, bulkheads 30 and/or tubular structures 14 are filled with a water-resistant and buoyant material (e.g., foam).

INDUSTRIAL APPLICABILITY

The disclosed arrangement and design of system 10 may be used to fabricate any multi-layer composite structure. The disclosed system 10 may be particularly useful for fabricating larg structures. System 10 may allow for rapid discharge of high volumes of material, with strong bonds between the layers. And the layers may have varied constructions (e.g., lattice-like skeletal layers, skin layers, coatings, etc.), use different materials, and have different sizes (e.g., thicknesses).

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed additive manufacturing system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed additive manufacturing system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. 

What is claimed is:
 1. An additive manufacturing system, comprising: a first print stage configured to discharge a first type of composite structure; a second print stage configured to discharge a second type of composite structure; and a support configured to move the first and second print stages.
 2. The additive manufacturing system of claim 1, wherein: the first type of composite structure is a tubular structure; and the second type of composite structure is a skin discharged adjacent the tubular structure.
 3. The additive manufacturing system of claim 2, further including a third print stage moveable by the support and configured to apply a finish coat to the skin.
 4. The additive manufacturing system of claim 3, wherein the first, second, and third print stages together fabricate an entire cross-section of a component.
 5. The additive manufacturing system of claim 4, wherein the component is a boat.
 6. The additive manufacturing system of claim 5, wherein: the first print stage is configured to anchor the first type of composite structure to an end of a bulkhead; and the second print stage is configured to extend the second type of composite structure over the first type of composite structure and over an outer annular surface of the bulkhead.
 7. The additive manufacturing system of claim 6, wherein at least one of the first and second print stages is further configured to fabricate the bulkhead in-situ.
 8. The additive manufacturing system of claim 6, wherein the bulkhead is pre-fabricated.
 9. The additive manufacturing system of claim 1, wherein: the first print stage includes a plurality of first print heads chained to each other; and the second print stage includes a plurality of second print heads changed to each other.
 10. The additive manufacturing system of claim 1, wherein the second print stage follows behind the first print stage a distance such that a matrix in the first type of composite structure is not fully cured when the second type of composite structure overlaps the first type of composite structure.
 11. The additive manufacturing system of claim 1, further including a controller in communication with the support and configured to regulate movements of the first and second print stages.
 12. A method of additive manufacturing, comprising: discharging from a first type of print head a first type of composite structure; and simultaneously discharging from a second type of print head a second type of composite structure adjacent the first type of composite structure.
 13. The method of claim 12, wherein: the first type of composite structure is a tubular structure; and the second type of composite structure is a skin.
 14. The method of claim 13, further including simultaneously applying a finish coat to the skin.
 15. The method of claim 14, wherein the tubular structure, skin, and finish coat together form a cross-section of a boat.
 16. The method of claim 15, further including: anchoring the tubular structure to an end of a bulkhead; and extending the skin over the tubular structure and over an outer annular surface of the bulkhead.
 17. The method of claim 16, further including discharging the bulkhead from a composite material in-situ.
 18. The method of claim 12, wherein: discharging from the first type of print head includes discharging from a plurality of the first type of print heads that have been chained to each other; and discharging from the second type of print head includes discharging from a plurality of the second type of print heads that have been chained to each other.
 19. The method of claim 12, further including moving the plurality of the second type of print heads to follow behind the plurality of the first type of print heads by a distance such that a matrix in the first type of composite structure is not fully cured when the second type of composite structure overlaps the first type of composite structure.
 20. A method of additive manufacturing, comprising: discharging a plurality of composite tubes adjacent each other to form an internal skeleton in a shape of a boat hull; and simultaneously discharging a composite skin over the plurality of composite tubes, wherein a matrix in the plurality of composite tubes is not fully cured when the composite skin is discharged over the plurality of composite tubes. 